RU202425U1 - ELECTRIC FURNACE FOR MELTING ELECTROLYTE CONTAINING FLUORIDE SALTS, USED IN ELECTROLYSERS FOR PRODUCING ALUMINUM - Google Patents

Abstract

The technical solution relates to electrometallurgy, and specifically to the electrolytic production of light metals: aluminum, magnesium. An electric furnace for melting electrolyte (fluoride salts), including a steel casing of the furnace bath with a lining of heat-insulating, refractory layers, the internal refractory lining of the furnace bath is protected from molten electrolyte (fluoride salts) from silicon carbide plates. The furnace is powered from the furnace transformer to the electrode through the electrolyte melt and to the carbon lining of the bottom of the furnace bath. Melting of the electrolyte (fluoride salts) is carried out in the resistance mode with the ratio of the electrode current to the voltage of 5300-10700. 1 ill.

Description

Technology area

The technical solution relates to electrometallurgy, and specifically to the electrolytic production of light metals: aluminum, magnesium.

State of the art

Aluminum is produced by electrolysis of an electrolyte melt (fluoride salts) in DC electrolyzers. Before starting a new bath of the electrolyzer, the bath is preheated in order to burn the hearth mass, which is filled with seams between the carbon blocks, then the required amount of molten electrolyte is poured into the bath. The electrolyte is pre-fused in existing electrolyzers, uterine baths (Borisoglebskiy Yu.V., Galevskiy GV and others. Aluminum metallurgy, Novosibirsk: Science, Siberian Publishing Company RAS, 1999, pp. 216-217). The disadvantage of this method of electrolyte melting is a decrease in the performance of electrolyzers, mother baths, an increase in electricity consumption for aluminum production due to the fact that the bulk of the supplied electricity goes to melting the excess electrolyte specially loaded into the electrolyzer for starting electrolyzers, and not to the electrolysis process.

A known salt-heated furnace for melting magnesium scrap (patent SU No. 1254830, F27B 19/02, publ. 10.05.96), including a lined casing with electrodes installed through the lining in the furnace shaft, electrodes are installed in the furnace at a distance from the hearth equal to 0 , 18 0.25 furnace shaft depth, and made protruding above the furnace lining into the shaft by 0.06 0.15 lining thickness. The furnace is additionally equipped with reserve electrodes, the number of which is equal to the number of working electrodes. Current leads are installed in the recesses of the outer lining. The disadvantage of the furnace of this design is the low service life of the furnace, rapid wear of the lining due to the presence of reserve electrodes. In addition, the design of the current lead does not provide uniform heating of the melt along the height of the furnace shaft.

Known furnace with salt heating for melting scrap of light metals (patent SU No. 1313088, F27B 14/00, publ. 20.06.96), containing a lined casing with electrodes installed and in the lining of the walls with output to the working space of the furnace bath. The lining of the furnace bath is made in the form of a solid concrete jacket, the lining of the hearth is made of mullite brick in contact with the melt, and the walls are made of blast furnace bricks. The disadvantage of the furnace is the insufficient service life of the furnace bath lining in the place where the electrodes pass.

Known electric furnace (RF patent No. 2089803, class F27B 3/08, priority dated 02.21.1996), containing an electric arc furnace with an electrically conductive hearth and an even number of furnace electrodes located on top and the number of power sources equal to the number of electrodes. The operation of the furnace is characterized by a developed arc mode and a decrease in charge conductivity currents. The disadvantage of this electric furnace is the developed arc mode of operation, which will lead to the evaporation of fluoride salts at the temperatures of the arc discharge.

Known electric furnace with salt heating (patent for utility model No. 74696, F27B 14/00, publ. 10.07.2008), consisting of a furnace shell with a lining of heat-insulating and refractory layers, stationary electrodes brought out through the lining by their ends into the working space at a distance from the bottom of the bath 0.1-0.15 height. The furnace is equipped with additional electrodes installed in the openings of the furnace bath overlap. The disadvantage of the furnace design is the low service life of the lining of the walls of the furnace bath made of mullite bricks and the uneven heating of the melt in the lower part of the furnace bath.

Known electric arc melting furnace (RF patent No. 2227881, F27B 3/08, publ. 04/27/2004), containing a bottom conductor located under the conductive part of the bath batch opposite the electrodes connected to a three-phase power transformer, with the organization under the electrodes of a concentrated ionized space in a limited volume , which provides a more stable mode of heating and melting of the metal.

By the technical essence, by the presence of common features, this technical solution is taken as the closest analogue.

The disadvantage of this furnace design is that the main operating mode of the furnace is arc, and this is unacceptable when the electrolyte melts, due to the increased volatility of the electrolyte (fluoride salts) at temperatures above 1000 ° C. Under arc conditions this will lead to significant evaporation of cryolite (fluoride salts).

The technical solution is based on the task aimed at increasing the stability of the electrolytic cells.

The technical result is to increase the productivity of electrolyzers.

Disclosure of a technical solution

The stated goal of the proposed technical solution is achieved due to the fact that the electrolyte (fluoride salts) for starting the baths is fused in a special electric furnace located in the electrolysis body. Voltage is supplied from the transformer to the carbon electrode and to the carbon current lead mounted in the bottom of the furnace bath. The electrolyte melt is formed due to the flow of current from the carbon electrode to the coal hearth through the electrolyte loaded into the furnace. The electrolyte melt is periodically drained from the furnace through a hole into the bath lining.

When conducting electrolysis of aluminum in an electrolyte melt (fluoride salts), the electric voltage at the anode-cathode section is 4.3-4.5 V, the current strength is 160,000 A (current-to-voltage ratio is 37200-35500). When solid particles (electrolyte or carbon) that have not been dissolved in the electrolyte enter, the contact between the anode and the electrolyte breaks at the interface between the anode and the electrolyte and spark discharges appear on the anode surface (“anode effect”). The discharges lead to an increase in voltage up to 15-30 V (the ratio of current to voltage 5300 at a voltage of 30 V, and 10700 at a voltage of 15 V) and, if this phenomenon is not eliminated, to evaporation (losses, changes in the composition) of the electrolyte and to further disruption of the regime electrolysis of aluminum (Cherkasova K.S. Aluminum production, GOU SPO Bratsk industrial technical school, Bratsk, 2008, p. 9). Based on the foregoing: the arc mode of operation of the furnace begins to develop, for electrolyzers with a current strength of 160000 A, in the range of the ratio of the electrode current to the voltage of 5300-10700.

Brief Description of Drawings

The essence of the utility model is illustrated in figure 1. The furnace for melting the electrolyte (fluoride salts) includes: a steel casing (1) with a heat-insulating coating, a refractory lining (2) with a protective layer (3) from the action of molten fluoride salts, made of silicon carbide plates , carbon lining of the hearth with elements for supplying current to the hearth (4), carbon electrode with a mechanism for moving the electrode (5). There is an opening (6) at the level of the bottom of the furnace bath for draining the molten electrolyte (8). The furnace is powered from the furnace transformer: to the current supply (7) of the carbon electrode (5) and to the current supply (9) to the bottom of the furnace bath (4).

Device operation

Melting of the electrolyte is carried out as follows. An electrolyte or other mixture of fluoride salts and a small amount of conductive materials, such as aluminum shavings, are loaded into the furnace on the hearth. The furnace is switched on under voltage in the resistance mode. After melting aluminum and obtaining electrolyte in liquid form, the electric current passing through the liquid electrolyte heats the melt, therefore, in order to avoid overheating, fresh portions of electrolyte are constantly loaded until the furnace bath is completely filled with liquid melt. After filling the bath and reaching the required temperature, the melt is drained, and the melt is moved in the ladle to be poured into the starting electrolyzer. When draining the melt, a small amount of the melt is left in the furnace bath for the subsequent electrolyte fusion cycle. The presence of molten electrolyte in the bath of the furnace does not lead to overheating of the electrolyte and its evaporation, accelerates the next melting cycle. During operation, when the electrode is constantly immersed in the melt, the operation of the furnace in the arc mode is excluded. The electrolyte is melted at a current-to-voltage ratio of 5300-10700. This ratio of the electrode current to voltage excludes the conduct of the electrolyte melting process with a developed arc mode.

The furnace tests carried out showed a sufficient level of electrolyte heating. The commissioning of the new baths took place without deviations from the current regulatory documentation for the commissioning of new baths. Electrolyzers, previously used as uterine baths, have maintained a stable production of aluminum.

Melting the electrolyte in a separate furnace made it possible to increase the productivity of the electrolyzer during the period of starting the electrolysers into operation. The capacity of electrolyzers with a current strength of 160,000 A, when the electrolyzer was operating in the bath-womb mode, was 1154 kg per day. When the electrolyzer was operating in stationary modes, the productivity of the electrolyzer was 1245 kg of aluminum per day; on average, the productivity of electrolyzers over a long period (fusion of electrolyte in uterine baths) was 1230 kg of aluminum per day. The increase in the productivity of electrolyzers was 15 kg of aluminum per day.

Melting of electrolyte and other fluoride salts in a single-electrode electric furnace of alternating current in the mode of electrical resistance with the ratio of electrode current to voltage in the range of 5300-107000, determines the novelty of the technical solution and meets the criterion "significant difference".

Claims (1)

An electric furnace for melting an electrolyte containing fluoride salts used in electrolyzers for producing aluminum, containing a furnace bath shell with a lining of heat-insulating, refractory layers, a current supply to the electrode and to the bottom of the furnace bath, and an oven transformer, characterized in that it is made with the possibility of providing electric power supply to the furnace from the furnace transformer to the electrode through the electrolyte to the hearth of the furnace when the ratio of the current (A) of the electrode to the voltage (V) equal to 5300-10700, and closing the electric circuit between the electrode and the hearth in resistance mode through the melt of said electrolyte its melting.

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